This invention relates generally to optical devices for redirecting a light beam at a prescribed angle relative to its incident direction, and, more particularly, to devices that redirect a light beam in a direction substantially normal to its incident direction.
Optical devices of this type are of particular use in rotating laser beam transmitters, which project a laser beam along a generally horizontal axis while rotating about a vertical axis. This defines a plane of light useful in numerous construction, agricultural and surveying applications.
An example of a prior optical device of this particular type is a pentagonal reflector device having a pair of five-sided side frames for mounting a two flat mirrors. The first mirror is oriented with its normal axis at an angle of about 22.5 degrees to the nominal axis of an incident beam, such that the beam is reflected toward the second mirror along an axis at about 45 degrees to the incident axis. The second mirror is oriented with its normal axis at about 22.5 degrees to that of the once-reflected beam, such that the beam is then redirected in a direction substantially normal to its incident direction. The pentagonal reflector device need not be critically oriented with respect to the incident light beam. The beam can impinge on the first mirror from a wide range of angles, and the device will still function properly to deflect the beam by 90 degrees.
Although the reflector device described above performs satisfactorily in most applications, its manufacture can be prohibitively expensive if extreme accuracy in the amount of angular deflection is required. FIG. 1 depicts one known apparatus for overcoming this prohibitive expense, while still achieving a high level of accuracy. The side frames and mirrors of this apparatus are formed with less precision, but the apparatus requires the addition of a wedge-shaped lens. The lens is rotated to a position such that it refracts the beam by an amount that compensates for the device's angular error. This solution is not completely satisfactory, however, because it requires inclusion of an additional optical element, and because this additional element can sometimes disperse the beam of light by an excessive amount.
It should therefore be appreciated that there is a need for an optical device for redirecting an incident beam of light by a prescribed angle that can be precisely selected without incurring prohibitive expense and without the need for a separate optical element. The present invention fulfills this need.